“Precipice”, “Cliff”, “Crag” + “Valley” or “Canyon”

Question

I wonder what word do you usually use in the following sense:

• Boy: What an astonishing scene. Come on; let's approach the its edge and take a selfie!
  Girl: no; let's not approach it. It is a dangerous...........
  

a. precipice
b. cliff
c. crag
d. canyon
e. valley

All the information I know:

• A "precipice" is a sudden steep drop. "Precipice" is a cliff with a vertical, nearly vertical, or overhanging face. a situation of great peril.
  A "cliff" may be precipitous but it can also have a gradually steepening slope leading to the vertical section. A "cliff" is a high steep face of a rock. Also, a "cliff" is a type of crag, and is always vertical (up and down), not horizontal (across, or stretching outward).

Also, dictionaries as usual cannot help me to tell these similar words apart:

Precipice: a very steep side of a cliff or a mountain.
Cliff: high area of rock with a very steep side, often on a coast.
Crag: a high, rough mass of rock that sticks out from the land around it.
Canyon: a large valley with very steep sides and usually a river flowing along the bottom.
Valley: an area of low land between hills or mountains, often with a river running through it.

Note: I would classify these five words as below:

1. Precipice - Cliff - Crag
   
2. Canyon - Valley

I know that the words in group #2 are more or less synonymous and are different from the words in group #1. But I needed two know whether I can use the words group two in this sense too or not. That was to avoid asking similar question plus making this thread more useful for other learners.

Answer 1

"Precipice" is surely the best word here, it means the very steep side of a mountain.

"Cliff" is also good, again it it indicates a near vertical drop.

"Crag" is probably no good in the example. It is a big rock that sticks up from the surrounding land. You won't be at the top of a crag, unless you are a mountain climber. I wouldn't say that a cliff is a type of crag, because the cliff isn't above the surrounding land.

"Valley" and "Canyon" are synonyms. A canyon has cliffs along the edge, a valley might have more gently sloping sides. But a valley is the low land, not the vertical drop. The valley or canyon isn't dangerous. The cliffs around the canyon might be dangerous.

So if you mean "It is dangerous because it is steep" then use "precipice". If you mean "It is a cliff that is dangerous (and cliffs are dangerous if they can collapse without warning)" then use "cliff".

A crag might be dangerous. "That's a dangerous crag, only experienced climbers should attempt it." But it doesn't fit your example.

A valley or canyon might be dangerous "There are lots of wild animals living in that valley, it is dangerous." There is a white water rapids in down that canyon, it is too dangerous for a canoe." But again, these words don't fit your example.